I'm interested in porting my Android applications to BlackBerry 10. I know it is possible to port to the PlayBook, but is this style porting also valid for BlackBerry 10?
Yes, Blackberry Playbook was built on QNX-OS, the same basis for Blackberry 10 (and the reason it is/will be upgradeable). You should be able to port any existing Android applications to Blackberry 10. You can either port the code directly, or port it using the Android App Player for Blackberry, both of which are explained in more detail at the links below.
Here's a link to some documentation on the process: http://developer.blackberry.com/native/documentation/bb10/porting_from_android_ndk.html
And finally, in case you've already ported to Playbook and want to port to BB10 now: http://developer.blackberry.com/android/documentation/port_android_app_pb_to_bb10.html